Airplane wing structure



mm. 31M W W. T. SCHWENDLER ETAL.

AIRPLANE WING STRUCTURE Filed March 12, 1946 4 Shets-Sheec l E my W5 W. T. sQHWENnLm mm. ZAM

AIRPLANE WING STRUCTURE Filed March l2, 1946 4 Sheets-Sheet 2 df/ @f JJ V11* W. T. SCHWENDLER ET AL 2,496,024

AIRPLANE WING STRUCTURE Filed March l2, 1946 4 Sheets-Sheet 5 n annuoooenoocoooocvcouoowno u oo oo o Qn oooouuuonosoocoooooooooooon Hmmm EL W, T, SCHWENDLER ETAL iill AIRPLANE WING STRUCTURE Patented Jan. 31, 1950 UNITED STATES PATENT OFFICE AIRPLAN E WING STRUCTURE Application March 12, 1946, Serial No. 653,806

,6 Claims.

This invention relates to improvements in airplane wing structures.

It is an object of the invention to prevent failure of the wings of an airplane due to accidental overload such as that produced by pulling abruptly out of a dive or for other reasons.

More specifically, it is an obiect of the invention to provide a wing constructed to withstand all designed loads with a margin of safety while at the same time it is provided with a safety feature whereby an outboard portion thereof may be cleanly shed under a predetermined load so as to relieve the inboard portions of overload. The remaining inboard portion shall be of dimensions suiiicient to enable the aircraft to be own and landed safely. This object is attained by constructing the wing in two or more sections in which an outer section is joined to its inboard member by a connection designed to fail or be disconnected in response to a predetermined critical load.

With the foregoing and other objects which will appear in the following full description in mind, the invention consists in the combinations and arrangements of parts and details of construction which will now iirst be fully described in connection with the accompanying drawing and then pointed out more particularly in the appended claims. The construction disclosed is `a practical embodiment of the invention, but it sponding to the encircled numeral 2 of Figure 1;

Figure 3 is a perspective view on an enlarged scale and with parts broken away showing wing structure just forward of the aileron and at a location corresponding to the encircled numeral 3 of Figure 1;

Figure 4 is a view similar to Figure 3 but showing an aileron hinge and associated structure, at

` a location corresponding to the encircled numeral 4 of Figure 1;

Figure 5 is an enlarged perspective viewof 2 the inboard section of the wing of Figure l, the tip section having been removed for clarity;

Figure 6 is a plan view on an enlarged scale of a portion of the wing of Figure l adjacent the line of separation and showing principally the separation of the wing covering or skin;

Figure 7 is a plan view on an enlarged scale, with parts omitted to show internal structure, of a portion of Figure 6 adjacent the encircled numeral I and showing the separation of inboard and tip aileron sections;

Figure 8 is a perspective view on an enlarged scale, adjacent the location 8 of Figure l, and showing the separation of the parts near the leading edge of the wing;

Figure 9 is an enlarged perspective, taken from another point of view adjacent the ilocation of the encircled numeral 2 of Figure 1, and showing the separation of the parts near the spanwise spar or beam;

Figure 10 is a view showing the joint structure at the location indicated by the encircle numeral l0 of Figure 1;

Figure 11 is a similar view showing the structure at the location indicated by the encircled numeral Il of Figure 1;

Figure 12 is a similar view showing the structure at the location indicated by the encircled numeral I2 of Figure 1; and

Figure 13 is a similar view but showing structure at the location indicated by the encircled numeral I3 of Figure 1.

It may be stated as a generality that an airplane wing forms a cantilever beam in which the bending moment increases continuously from the tip up to, or substantially up to, the juncture of the wing with the body of the aircraft. Although the lift contributed by a relatively small portion of the tip of the wing may also be relatively small, the contribution of such tip section to the totalV bending moment at an inboard point will be very large by comparison with the contribution of an inboard wing section producing comparable lift. It, therefore, becomes possible to relievel the wing from bending stresses, which might otherwise cause failure, by removing a tip section with a corresponding loss of lift which is, however, relatively very small. In other words, a large percentage reduction of bending moment at a possible inboard fracture point may be accomplished at the expense of a much smaller percentage reduction in over-all lift. Althoughl wings may be designed for a wide variety of strengths under normal conditions, and a wing tip may be designed to be shed at any predetermined `limit of overload, the principles involved are' thesame, and accordingly only a single set of conditions` requires discussion for a full understanding of the invention. For example, it may be assumed for deniteness that the major elements of the wing are designed to withstand wing loads corresponding to'pull .puts producing centrifugal force "above -nine times gravityjwhile the connection between the louter or tip section and the inboard section may be designed to fail at nine .gs, causing the tipsectionto be shed, and such design will permit the inboard portion of the'wing to withstand wing loadscorresponding totwelve `gs or more, depending `upon the amount of reduction of the span'offthe wing The wing strength for normalmlying 'conditions' the .failure load of the connection and the strength of the inboard section with the tip secy tion removed may be specified, if desired, :in terms of the load upon the wing. Such load, however, is in any given `'constructionitself a function of centrif-ugaliforc'zey or,where .not PrO- duced by a pull out, is translatable into such terms, so lthat a c'ompletei-description of wing strengthcan be made in theforegoing terms.

Due to 'the difference, incontribution of a tip section tolift and to bending moment, it is pos- 1sible with any given vdesign of aircraft to inn lsure adequate liftfor safeflying and safe landling with a tipsection removed, since the wing as a whole will normally .be so constructed as to provide the excess liftwhich is necessary dur- Aing take-offs and rapid climb.

:"Referring now to Figure .1, the wing com-prises an inboard section 20 including a xed trailing edge 2|, an outboard wing tip section 22, an inboard hinged aileron section 23 and anvoutboard hinged aileron tip section 24. The wing is designed to break alongthe joint between sections 20 and 23, on the one hand, Aand 22 and 2li, on .the other hand, and .thus breaks through the aileron. As will beapparentifrcm-the following description, however, the invention may also be applied so as to break through a wing section having no hinged .parts Yor through a wing section having ilaps or any other hinged elements instead of a hinged aileron.

Although the invention in its broader aspects is applicable to wings offpractically any desired design, it is shown for ,clarity and simplicity only g as'applied to 'a single spar wing structure. Bas ically, all wing structural members 'are tei-mie members or ribs 33 and 33', respectively fore and aft of the main spar, and which may be of any convenient form. These elements form an enclosure for the end of the inboard wing section. The upper and lower edges of the members 33 and 33' are provided with flanges in the usual way, Vto which flanges are attached the structural joint elements hereinafter described, and are also provided with apertures, as shown, to accommodate the spanwise Stringer and main '.tachment is permanent.

; In Figure 10, a portion of the chordwise member 3 3 `is shown together with a portion of the upper iiange ,Sithereof The upper ange 34 is Vvrecessed to receive the inboard Stringer |25 which may be riveted or welded thereto, since the at- Y A further chordwise member 35 is attached to the flange 34 and above the Stringer |25 and may be fastened at this 'point by riveting through both me-mbers 34 and `|25, as indicated. The'member 35 isfurther provided with projecting tabs 36in alinement with ,Stringer |25, and to which the Stringer 25 vmay be riveted as indicated. The tabs 33 are set l stringer |23 by means of rivet 31 passing through nated ,where the. intended ,separation is to occur y 'and yform a complete` wing inboard ovthis locaV-Lk tion.` Further structural elements: are connected* to form contihuations of- ,the inboard elements` v vi'nboard or main Vwing section by attaching the ends of them-ain spar and ystringers to corre,- sponding inboardv sections. The corresponding inboard elements are identified in casali-frail.r views! byy correspondingv reference numeralsl in"-l creased by one` hundred. and'will be described in conjunction with those views. f

The inboard or mainA wing' section.` terminates, as best shown in Figure 5, in chordwise structural thev wing: tip .22 is sup-`V i board spar |32.

the webs-of the two members. The web-0f Stringer ZBfpasses through an aperture in the member 33 as indicated, the end of the web being shaped, and the Vfiange being depressed'as indicated, so as to permit the same to pass underv chordwise member 35. In addition to the attachment of the webs of-members 2B and |26 by the rivet 31,'their respective iianges -are also riveted to the member 35 and flange 34, as indicated. Figure llshows alsothe attachment of a-lower tip stringer'member- 38 to an inboard Stringer member |38, which,

- being symmetrical with the upper member and being attached in -a similar way, requires no further description. Figure 8 shows the mode of separation of the wing sections adjacent lthe Stringer 26-|26.

Figure 41,2, and also Figures 2 and 9, show the joint at. the main spar. The member Y33 terminates at this joint and ythere is 4aixed to it an angle 39 which is riveted to the web of the in- A similar angle 4Q is likewise riveted to the aft chordwisey member 33 and tot-he web ofthe spar |32, the two angles 39 and 40 forming a slot outboard of the spar |32 into which the. web of the spar 32 is inserted and held by rivets as shown. A further strengthening plate` 4| is provided on top of the flange 34 below the member 35 and the flange of the spar |32 is riveted to this member which thus, in effect, forms an extension of the flange 34 at this point. The ,iangeV ofr the spar 32 passes under the top` of the, member 35 but is notrlveted thereto. Chordwise member 34' which extends aft fromthe main spar is similarly fastened' thereto and provided with a strengthening plate 42 similar to the p1 ate 4| and' hence requires no further description.` Fig;- ure 9 shows the parts adjacent the main spar joint from anv inboard point of view andV in the act off breaking apart; the line of rivets which break orare forced outbeing` indicated byloose rivets adjacent the rivet holes.

'Figurev 13 shows the joint which is employed in connection with the stringer 29. This view shows the rearward chordwise member 33', the upper iiange 34 thereof together with rearward joining plate 35 and stiifening member and the inboard and outboard Stringer sections |29 and 29. The mode of attaching the sections together being similar to that of Figure 10, with the eX- ception of the addition of the plate (l2, Will be clear from the description of that figure.

The structure adjacent the aileron is shown in Figures 3 to '7. As there shown, the outboard wing section terminates in a curved plate 59, behind which the aileron is hingedly supported, and this element is contnued inboard of the rib 33 by a similar element, not shown. The aileron is supported from the wing sections by hinges spaced along its length, only one of these hinges, 5|, being shown. The hinge 5| includes a member l52 fastened to the Wing section behind plate 53 and a member 54 supporting the aileron and attached to spanwise structural member H55 thereof. The inboard portion of the aileron includes a fabric partition covering 53 which serves to enclose its end when the outboard section is removed. Where a fabric covering aileron is utilized, the fabric is merely permitted to tear when the Wing tip comes off, as indicated in Figures 5 and 6, being attached to the structural elements shown in Figure '7, `and in particular to chord- Wise members, such as the member 51 and 58, which serve to define a line of separation. The rigidity of the structure adjacent the aileron is increased, without interfering with the separation of the parts, by pins 59 (Figure 5) which pass through apertures in the angle 60 (Figure 3), and prevent twisting of the parts. In general. it is preferred to join the lower Stringer elements only by the Webs thereof, as indicated in Figure 8, but additional strength adjacent the aileron. or in any other desired location, may be provided, as by means of plate Bl (Figures 3 and 5) to which the tip section 22 is attached.

In breaking, the tip section works on its upper edge as a fulcrum and breaks its inboard lower stringer joints (Figures 8 and 11). By making the rivet connections of suitable strength, the fracture load may be closely controlled. Continuing its movement, the tip section Will separate at the main spar (Figure 9) and along its upper edge, the stress being progressively placed upon the various fastening elements, and will tear ofi", carrying the outboard aileron section 24 with it, by means of the hinge connection therein.

The skin parts along the line indicated in Figures 5 and 6, the outboard skin element being riveted to members 35 and 35' previously referred to and to similar members on the lower surface. not shown. The skin fastening is carried around the leading edge of the wing by element 62. to which the skin is also riveted. As will be understoodA the fracture strength of the joint, including the skin riveting, will be such as to provide for separation at the desired wing loading.

What is claimed is:

1. An aircraft Wing comprising a main. inboard section terminating in a chordwise rib forming an enclosure for the end thereof, a tip section., the said inboard and tip sections having aligned spanwise structural elements, a fastening plate iii) attached to said rib and to spanwise structural elements of the said inboard section, and means joining spanwise structural elements of the two said sections together and to the said fastening plate, the said means being breakable under a Wing load within the safe load for the other elements of the wing.

2. In an aircraft wing of the type described, an inboard spar section, an outboard spar section, and means joining the said sections together and comprising angle members fastened to the inboard section and forming a slot for receiving the inboard end of the outboard section, and breakable means fastening the outboard section in the said slot.

3. In an aircraft wing of the type described, chordwise structural elements forming an inclosure for a main inboard wing section, a spar inboard of the said chordwise elements, a spar outboard of the said chordwise elements and continuing the said inboard spar, angle members joining the said inboard spar and chordwise elements and forming a slot for receiving the inboard end of the outboard spar, and breakable means fastening the outboard spar in the said slot.

4. In an aircraft wing of the type described, a rib forming an enclosure for a main inboard wing section, a spanwise structural element inboard of the said rib and connected thereto, a spanwise structural element outboard of the said rib and having a web extension passing through an aperture in the said rib, and breakable means attaching the said web extension to the rst said spanwise element.

5. In an aircraft wing of the type described, a flanged rib forming an enclosure for a main inboard wing section, a spanwise structural element inboard of the said rib and fastened to the flange thereof, a fastening plate above said flange and also fastened thereto, and a spanwise structural element outboard of the said rib and breakably fastened to the said plate.

6. In an aircraft wing of the type described, a

' main inboard spar section, a tip spar section, rib

elements fore and aft of said spar sections, and means joining said rib elements and spar sections together and comprising means for permitting separation of said tip spar section in flight.

WM. T. SCHWENDLER. OSCAR ERLANDSEN, JR.

REFERENCES CITED The following references are of record in the .die of this patent:

UNITED STATES PATENTS OTHER REFERENCES Report oi Civil Aeronautics Board, file No. 2,905, Docket No. SA-'78, published October 11, 1943, page 19. (Copy in Div. 22.) 

